Various types of protective apparatus and systems are known in the prior art. The following U.S. Pat. Nos. are believed to represent the state of the art: 5,986,549; 5,767,672; 5,760,577; 5,731,785; 5,656,998; 5,519,317; 5,264,733; 5,241,297; 5,237,307; 5,191,314; 5,012,206; 4,897,531; 4,857,892; 4,587,486; 4,458,241; 4,391,203; 4,359,717; 4,274,088; 3,973,191; 3,579,222.